This data release documents the data and models used to assess flows, concentrations, and loads of highway and urban runoff and of stormwater within receiving streams in southern New England. There are more than 48,000 locations in southern New England where roads cross streams and many more locations where runoff from developed areas may discharge to receiving streams; information about runoff discharges and the quantity and quality of stormflow upstream and downstream of discharge points is needed to inform resource-management decisions. This analysis was done with a version 1.1.1 of the Stochastic Empirical Loading and Dilution Model (SELDM) that was populated with regional statistics for southern New England. SELDM uses basin properties and hydrologic statistics to simulate runoff from a site of interest, which may be a highway site or another developed (urban) area, and concurrent stormflow from an upstream basin to calculate downstream values, which are the sum of contributions from the site of interest and the upstream basin. Because there are few monitoring sites with data relative to the number of potential sites of interest, the probability that data will be available at a site of interest is low. Furthermore, much of the data available at monitored sites is not sufficient to characterize long-term stormwater-quality conditions because most water-quality monitoring sites have less than one year of data. The statistics for highway and upstream basin properties, hydrologic variables, and stormwater quality provided in this data release can be used to represent long-term conditions throughout southern New England. The simulated populations of flows, concentrations, and loads documented in this data release represent long-term conditions at representative sites of interest. This data release also documents results of sensitivity analyses designed to guide the selection of input variables for runoff quality simulations and selected example simulations that illustrate use of simulation results for decision making. The methods and statistics in this study were developed for use with SELDM but may be used with other models. The information provided here can be used for robust decision making by highway practitioners, regulators, and decisionmakers. The project described in this data release was conducted in cooperation with the Federal Highway Administration and the Connecticut, Massachusetts, and Rhode Island Departments of Transportation. The data release contains twenty-one compressed (zip) files, one ReadMe file pertaining to the data release as a whole (ReadMe.txt), and a diagram to illustrate the organization of the zip files and subfolders (ReadMeDiagram.pdf). Please refer to ReadMe files within the zip files and subfolders for more detailed metadata pertaining to the data, statistics, and software provided.